A metal phthalocyanine compound is a useful compound as a material for paint, printing ink, colorant, electrophotosensitive material or body, or optical disc, and hitherto a great many compound have been synthesized and produced. Industrial production of the metal phthalocyanine compound is described in detail in “Phthalocyanine-Kagaku to Kino-”, written by Hirofusa Shirai and Nagao Kobayashi, published by Industrial Publishing & Consulting, Inc. (1997). The industrial production of the metal phthalocyanine compound is roughly classified into two methods.
1) Weyler Method:
This method employs phthalic anhydride or phthalic anhydride imide as a raw material and involves a reaction of urea and a metal salt at 160° C. to 180° C. in the presence of a condensation agent for production of a metal phthalocyanine compound. An arsenic-series inorganic salt has been heretofore used as a condensation agent, but in recent years, a molybdate is generally used. This method includes, as a solid phase method, a method in which a urea melt is used as a solvent. However, the solid phase method is not preferred as a method for mass production, because of risk of foaming, disadvantages due to solidification during temperature decrease, low yield, and formation of large amounts of impurities in a product.
Meanwhile, a liquid phase method employing an inert organic solvent, such as nitrobenzene or polyhalogenated benzene, provides higher yield and tends to provide more stable quality than those of the solid phase method. The liquid phase method is the main stream of a current method for industrial production of phthalocyanine. However, this liquid phase method requires complex unit operations such as separation and recovery of a reaction solvent. Further, the liquid phase method has problems in safety in that nitrobenzene is toxic and polyhalogenated benzene forms small amounts of toxic substances such as halogenated biphenyl as by-products. Thus, selection of an appropriate high-boiling-point solvent is one of tasks to be solved by the method for industrial production of phthalocyanine.
2) Phthalonitrile Method:
This method employs highly reactive phthalonitrile as a starting material. This method includes: a method referred to as a solid phase method or a baking method, which involves heating of a mixture of phthalonitrile and a metal salt and using molten urea as a solvent; and a liquid phase method, which involves heat condensation of phthalonitrile and a metal salt in an appropriate high boiling point solvent. In this case, quinoline or the like has been preferably used as a basic solvent for its condensation acceleration function, but industrial use of quinoline or the like must be avoided at present from a viewpoint of safety. Selection of a solvent is also one task in this method, similar to that in the liquid phase method of the Weyler method. A price of phthalonitrile is about ten times that of phthalic anhydride, and this method has a disadvantage in that a raw material cost of this method is much higher than that of the Weyler method. However, this method is an optimal method for recent production of functional phthalocyanine having high added value when emphasis is placed on various merits in production, even in consideration of terminal price of a product.
Further, JP-A-49-49759 (“JP-A” means unexamined published Japanese patent application) discloses a method of relaxing reaction conditions in this phthalonitrile method by using a base. For example, JP-A-49-49759 describes that copper phthalocyanine can be obtained in high yield through a reaction of phthalonitrile and cuprous chloride in ethylene glycol under ammonia bubbling at a temperature of about 100° C. Further, various phthalocyanines are industrially produced by using as a condensation agent of a high-boiling-point amine, such as a secondary or tertiary amine, instead of ammonia as a base. The specification of Japanese Patent No. 2,520,476 discloses a general method for industrial production of nonmetal phthalocyanine, and this method employs, as a condensation agent, a high-boiling-point amine, such as tributylamine, diazabicycloundecene, and diazobicyclononene, as an amine, in addition to an alcholate.
However, use of such a relatively strong base may cause decomposition of some kinds of phthalonitrile, and provides a disadvantage of degrading yield of a target phthalocyanine compound. For example, phthalonitrile having an electron withdrawing group substituted causes a concerted reaction of an intended condensation reaction and a decomposition reaction due to attack on phthalonitrile by a nucleophilic reagent such as a hydroxide ion, and thus a condensation rate of a metal phthalocyanine compound is not improved. Further, in production of a metal phthalocyanine compound by using a metal chloride, hydrochloric acid is produced with progress of condensation, and hydrochloric acid inhibits the attack by a nucleophilic species serving as a catalyst for condensation. Thus, the progress of the condensation reaction gradually slows down, and the reaction eventually stops even if the raw material remains. In this case, a target substance alone is hardly isolated from a reaction mixture through a recrystallization or reprecipitation method, which may appropriately be used for production, and a purification method involving column chromatography which has low production efficiency is required. Thus, this method has a disadvantage of an extended production process, leading to cost increase from an industrial viewpoint.
There are known: a method involving a reaction by using a high-boiling-point alcohol (such as n-butanol) solvent in the presence of a strong base such as DBU, as disclosed in JP-A-11-269399; and a method involving use of a metal alkoxide, as disclosed in JP-A-11-209380. However, a reaction system in each of the methods is strongly basic, and a substrate having a substituent that is easily decomposed under basic conditions cannot be used. Further, a reaction substrate may decompose owing to water contained in the reaction substrate or solvent, and a yield may be reduced significantly.
Further, there are also known: a method involving a reaction in the presence of a dehydrating agent, as disclosed in JP-A-11-116835; and a method involving a reaction in the presence of a metal oxide and an acid having a pKa of 7.0 or less in combination, as disclosed in JP-A-11-263919. Those methods provide improved yield, but the yield is currently not at a satisfying level. JP-A-2000-169743 discloses a method of producing a phthalocyanine compound in the presence of an alkali earth metal compound, but this method has problems in yield and purity.
There is known an economic production method, as disclosed in JP-A-2005-41856, with significantly improved reactivity and purity for solving the above-mentioned problems, but there is a need for further improvement in yield and a method of improving operability (reduction in reaction time, crystallinity, filtration property, or the like) on a production scale.
Further, a phthalocyanine compound and an analogue thereof each find use in a wide variety of applications including a dye or pigment having high fastness and a functional colorant. In recent years, introduction of various substituents into the phthalocyanine compound has been demanded strongly for providing enhanced functions, but such a demand cannot necessarily be met through currently known synthesis methods.
For example, there are known: a method involving a reaction by using a high-boiling-point alcohol (such as n-butanol) solvent in the presence of a strong base such as DBU, as disclosed in JP-A-11-269399; and a method involving use of a metal alkoxide, as disclosed in JP-A-11-209380. However, a reaction system in each of the methods is strongly basic, and a substrate having a substituent that is easily decomposed under basic conditions cannot be used. Further, a reaction substrate may decompose owing to water contained in the reaction substrate or solvent, and a yield may be reduced significantly. Further, there are also known: a method involving a reaction in the presence of a dehydrating agent, as disclosed in JP-A-11-116835; and a method involving a reaction in the presence of a metal oxide and an acid having a pKa of 7.0 or less in combination, as disclosed in JP-A-11-263919. Those methods provide improved yield, but the yield is currently not at a satisfying level.